Axial Piston Machine with Neutral Valve Integrated in the Pot-Like Housing Part

This application claims priority under 35 U.S.C. § 119 to application no. DE 10 2024 203 205.0, filed on Apr. 9, 2024 in Germany, the disclosure of which is incorporated herein by reference in its entirety.

The disclosure relates to an axial piston machine.

From the data sheet “Axialkolben-Verstellpumpe A4VG Baureihe 40” of Bosch Rexroth AG (order number RD92004; edition 30 Mar. 2020), an axial piston machine in a swashplate design is known, the displacement volume of which is adjustable by means of a double-acting control cylinder. In the variant “ET-adjustment”, the control cylinder is adjusted with two pressure-reducing valves, which are mounted on the outside of the control cylinder. Optionally, the control cylinder may be equipped with a neutral valve, which is mounted on the exterior of the control cylinder. With the neutral valve, both control chambers of the control cylinder may be connected to the substantially unpressurized interior of the housing, such that the displacement volume adjusts to zero, regardless of the adjustment of the pressure-reducing valves. The control cylinder is supplied with pressurized fluid from an auxiliary pump integrated into the axial piston machine.

From the data sheet “Axialkolben-Verstellpumpe A4VG Baureihe 35” of the Bosch Rexroth AG (order number RD 92035, edition Dec. 2, 2020), a similar axial piston machine is known, which can also be configured with an ET adjustment. The pressure-reducing valves therein are configured as built-in valves, which are installed directly in the pot-like housing part, which also houses the control cylinder. This axial piston machine cannot be equipped with a neutral valve. Not even if a plurality of bores are subsequently inserted into the pot-like housing part to provide the required connections.

The present disclosure has the advantage that the axial piston machine may or may not be equipped with a third control assembly in the form of a neutral valve as per customer request. Moreover, a plurality of further adjustment variants may be provided, solely by selecting the corresponding built-in valves. Regardless of the installation variant selected, the same pot-like housing part can be used without having to remachine it for each order. It can therefore be manufactured inexpensively in large batches. An expensive supply of different variants of the pot-like housing part can be dispensed with.

According to the disclosure, it is proposed that the transfer point is the point of the fluid flow path at which the plate-like housing part contacts the pot-like housing part, wherein the receiving bore of the first, the second and the third control assemblies are each arranged directly in the pot-like housing part, wherein the part of said fluid flow path, which is arranged downstream of the transfer point, extends over its entire length directly in the pot-like housing part. The receiving bores of the first and the second control assembly are preferably identical to each other. The first and/or the second and/or the third control assembly is preferably configured as a built-in valve.

It may be provided that the receiving bores of the first, the second and third control assembly each define a central axis, wherein the relevant return point, the relevant outlet point and the respective inlet point are each arranged in the order indicated along the respective central axis, wherein the respective feed point is arranged on a side of the respective receiving bore which is open towards the surroundings of the axial piston machine. All three return points are thus arranged adjacent to the interior of the housing so that the corresponding connection can be easily established. The connection between the return points of the first, the second and the third control assemblies and the interior of the housing preferably runs exclusively in the pot-like housing part. The aforementioned receiving bores are preferably configured as stepped bores, wherein the return point, the outlet point and the inlet point have different diameters.

It may be provided that a control piston of the control cylinder is linearly movable along a control axis, wherein the control piston segments the first and second control chambers from each other, wherein the first, third and second control assemblies are arranged next to each other in a direction parallel to the control axis in the specified order. Accordingly, the third control assembly is arranged between the first and second control assemblies. The third control assembly does not increase the required installation space for the entire axial piston machine. The bores in the pot-like housing part explained below are simple and inexpensive to manufacture. The paths from the first and second control assemblies to the first or second control chambers are very short. The control axis is preferably arranged perpendicularly and at distance to the axis of rotation of the axial piston engine.

It may be provided that the inlet point of the first and second control assemblies and the outlet point of the third control assembly are arranged in alignment with one another in a direction parallel to the control axis, wherein the corresponding portion of the fluid flow path is formed exclusively from a straight first bore, which directly intersects the inlet point of the first and second control assemblies and outlet point of the third control assembly in each case. Thus, a lengthwise large proportion of the fluid flow path is formed from a single straight first bore. This can be drilled into the overall complex pot-like housing part easily and inexpensively.

It may be provided that the receiving bore of the third control assembly directly opens out into the interior of the housing. Accordingly, the return point of the third control assembly is permanently fluidly connected to the interior of the housing by the shortest route. In the area of the third control assembly, a small wall thickness of the pot-like housing part is sufficient to provide the corresponding receiving bore. In the first and second control assemblies, the corresponding connection to the interior is preferably provided via a respective associated channel in the pot-like housing part, because they are arranged far outwards on the pot-like housing part.

It may be provided that the said fluid flow path between the transfer point and the inlet point of the third control assembly is formed exclusively from a straight second bore. The second bore may be drilled from the transfer point. A separate locking screw for the second bore is not required.

It may be provided that the first and second bores are arranged substantially perpendicular to each other, wherein their central axes are arranged spaced apart from each other.

It may be provided that the third control assembly is formed from a blind plug which permanently establishes a fluidic connection between the respective inlet point and the respective outlet point, wherein it permanently blocks the respective return point. With the blind plug, an installation variant of the axial piston machine may be provided that is not equipped with the neutral valve. It would now be conceivable to provide a variant of the pot-like housing part, in which the second bore directly opens into the first bore, wherein the blind plug and the associated receiving bore are omitted. However, it has been shown that the small cost disadvantage caused by the named receiving bore and the blind plug is more than offset by the cost advantage associated with larger batches in the manufacture of the pot-like housing part and by lower storage costs.

It may be provided that the third control assembly comprises a 3/2-way valve. The 3/2-way valve provides the function of the neutral valve explained above. The 3/2-way valve is preferably electrically actuated, wherein in a spring-biased base point, the fluid connection from the inlet point or from the return point to the outlet point is optionally open, wherein the respective remaining connection point, namely the inlet point or the return point, is blocked.

Of course, the above-mentioned features and those to be explained below can be used not only in the combination indicated in each case, but also in other combinations or on their own, without going beyond the scope of the present disclosure.

shows a perspective view of an axial piston machineaccording to the disclosure. The axial piston machinecomprises a housing, which is composed of a pot-like housing partand a plate-like housing part. The two housing parts;are fixedly connected to one another, in particular screwed together, wherein they abut one another against a contact surface, wherein they surround an interior (no.in). In the present case, the contact surfaceis flat, wherein it is arranged perpendicular to the axis of rotationof the drive shaft.

The first and second working connections (No.;in) are arranged on the plate-like housing portion, wherein the auxiliary pump (No.in) is arranged within the plate-like housing portion. The auxiliary pumpmay be configured as an internal gear pump, for example.

An axial piston engine (No.in) is arranged in the interior of the housingand is in rotational drive connection with the drive shaft. In the present case, the axial piston engine is configured in a swashplate design with a continuously adjustable displacement volume. The corresponding swivel cradle is coupled to a moving control cylinderto adjust the displacement volume. The control piston (No.in) of the control cylinder moves linearly along the control axis. The control axisis configured perpendicular to the axis of rotation, wherein it is arranged at distance thereto. The control cylinderis arranged in the pot-like housing part, wherein a first, a second and a third control assembly;;are arranged therein. These are each configured in the form of built-in valve, which is accommodated in an associated receiving bore (No.;;in). The aforementioned receiving bores are arranged directly in the pot-like housing part. In the present case, the built-in valves are each fastened with two fastening screws, which are configured as cylinder head screws, for example. For this fastening variant, the depth of the receiving bores is particularly low.

The mentioned built-in valves are commercially available valves that have not been modified for the present axial piston machine. The disclosure makes use of the corresponding receiving bores being standardized so that different built-in valves can be installed in the same receiving bore. In, the first and second control assemblies;are each configured as a pressure-reducing valve, which have a rising characteristic curve, for example (see). The third control assemblyis configured as a 3/2-way valve, which has a closed home position, for example (see). All three control assemblies;;are electrically adjustable by means of an electromagnet.

The valve assembly discussed above is a frequently found variant. However, other variants are contemplated. In particular, the third control assemblymay be replaced by a blind plug (see). Only one pressure-reducing valve may be used with the first and second control assemblies;, wherein the other control assembly, namely the second or the first control assembly, are configured as a 3/2-way valve. Regarding the advantages of this variant, reference is made to DE 10 2023 210 958 B3 and DE 10 2023 210 960 B3, the contents of both which are incorporated by reference herein in their entirety. Furthermore, it is contemplated to configure both the first and second control assemblies as a 3/2-way valve.

One particular advantage of the present disclosure is that all of these variants can be provided without requiring special machining of the pot-like housing part. The pot-like housing partis configured exactly the same in all variants. It can therefore be manufactured and stocked in large batch sizes as part of the series production of the axial piston machine, wherein it does not have to be manufactured or remachined individually for each order. This results in significant cost savings. The additional machining work necessary for this on the pot-like housing part within the context of the disclosure is very small. Accordingly, the axial piston machineaccording to the disclosure can already be manufactured more economically than the known axial piston machine previously explained, even with low quantities.

In the area of the control cylinder, a first, a second, a third and a fourth measuring connection;;;are arranged, which are typically tightly sealed by a locking screw, wherein they are used, for example, during the testing of the axial piston machinein order to measure the pressures explained below. At the first or second measuring connection;, the pressure is applied in the first or second control chamber (no.;in). The output pressure of the third control assemblyis present at the third measuring connection. The pressure in the interior of the housingis present at the fourth measuring connection.

Reference should also be made to the return connectionon the housing, which is also connected to the interior in order to drain the leaks or other oil quantities occurring there to a tank. The housingpreferably has a plurality of such return connections, which are arranged at different points, in each case using the return connectionwhich is arranged lowest with respect to the direction of gravity.

shows a hydraulic circuit diagram of the axial piston machineof. The axial piston engineand the auxiliary pumpare in rotational drive connection with the common drive shaft, with the drive shaftbeing driven by, for example, an electric motor or an internal combustion engine. The axial piston engineis connected to the first and second working connection;, wherein it is designed for use in a closed hydraulic circuit. The displacement volume can therefore be adjusted beyond zero so that the conveying direction can be reversed simply by adjusting the swivel cradle. Furthermore, depending on the operating state, either of first or second working connections;may carry high pressure, wherein the other, second or first, working connection;carries low pressure. This is also referred to as 4-quadrant operation.

The auxiliary pumpdraws in pressurized fluid from an inlet connectionon the housing. The pressurized fluid is preferably a liquid and in particular hydraulic oil. In the present case, the auxiliary pumpalso serves to flush the aforementioned closed hydraulic circuit in order to avoid overheating of the pressurized fluid. Furthermore, unavoidable leaks in the closed circuit are replaced by the auxiliary pump. The feed/flush valve assemblyis used for this purpose.

Moreover, the auxiliary pumpsupplies the adjustment of the control cylinderwith pressurized fluid. The control cylinderis configured as a double-acting cylinder, comprising first and second control chambers;, which segment each other by a linearly movable pistonalong the control axis (no.in). The pistonis movably coupled to the swivel cradle of the axial piston engine.

The first control chamberis permanently connected to the outlet pointof the first control assembly;″;″;′″. The first control assembly;′;″;′″ may be optionally configured according to any one of;;or, which is why the corresponding box inis shown empty. The second control chamberis permanently connected to the outlet pointof the second control assembly;″;″;′″. The second control assembly;′;″;″″ may be optionally configured according to any one of;;or, which is why the corresponding box inis shown empty.

Starting from the auxiliary pump, a fluid flow path passes via a transfer point, further via the inlet pointof the third control assembly;′;″, through the third control assembly;′;″ to the outlet pointof the third control assembly′;′;′ and finally parallel to the inlet point;of the first and the second control assemblies;′;″;″′;;′;″;″′. The third control assembly;′;″″ may be optionally configured according to any one of;or, which is why the corresponding box inis shown empty.

When the third control assembly′;″ is configured as a 3/2-way valve, it serves as a so-called neutral valve, which is used for operational safety. In the so-called closed position of the neutral valve, both the first and second control chambers;are connected to the substantially unpressurized interior of the housing so that the swivel cradle moves to the position in which the displacement volume is zero. In the open position of the neutral valve, the normal adjustment of the displacement volume takes place by means of the first and second control assemblies;′;″;″′;;″;″;″′.

shows a hydraulic circuit diagram of a first, second or third control assembly″;″;, respectively, comprising a 3/2-way valvewith a closed home position. The home position is the left position in, which is biased with a spring. In the closed position, the connection from the inlet point;;to the outlet point;;is blocked, wherein the outlet point;;is instead connected to the return point;;.

The open position is the right position shown in, which can be adjusted by energizing the electromagnet. In the open position, the connection from the inlet point;;to the outlet point;;is open, wherein the return point;;is blocked.

Reference is still made to the filters, which may be provided at the inlet point;;and at the outlet point;;. These can be configured as wire fabric or as a perforated sheet.

shows a hydraulic circuit diagram of a first, second or third control assembly″′;″′;′, respectively, comprising a 3/2-way valvewith an open home position. This is identical to the embodiment according toexcept for the actuating direction, so that reference is made in this regard to the statements regarding.

The left position biased by the spring, on the left in, is now the open position, wherein the position adjustable by the electromagnet, in the right in in, is the closed position.

shows a hydraulic circuit diagram of a first and second control assembly;, respectively, comprising a pressure-reducing valvewith rising characteristic curve. The pressure-reducing valveis similar in structure to the 3/2-way valve of, wherein the transition between the open and closed positions are continuous. Moreover, the pressure at the outlet point;acts on the corresponding valve slider towards the closed position. When a balance of forces has been established at the valve slider, the pressure at the outlet point;corresponds to the pressure equivalent of the magnetic force of the electromagnet minus the force of the spring. The aforementioned pressure therefore increases with increasing current in the electromagnet, therefore one speaks of a rising characteristic curve. The biasing force of the spring is preferably designed to be low, ensuring that the closed position is set when electromagnetis de-energized.

shows a hydraulic circuit diagram of a first and second control assembly′;′, respectively, comprising a pressure-reducing valvewith falling characteristic curve. Apart from the differences explained below, this first or second control assembly′;′ is identical to that of, so that reference is made in this regard to the statements of.

The springis now configured with a high biasing force, wherein it acts on the valve slider towards the open position. For currentless electromagnets, there is therefore a maximum possible pressure at the outlet point;, namely substantially the pressure at the inlet point;. The electromagnetis installed in such a way that it acts against the biasing force of the spring, so that the pressure at the outlet point;can be lowered by energizing the electromagnet. A falling characteristic curve is therefore referred to.

shows a hydraulic circuit diagram of a third control assemblyin the form of a blind plug. The blind plugis installed in the corresponding receiving bore (no.in) in the same way as the built-in valves described above, wherein it is configured as a rigid body. It establishes a permanent connection between the inlet pointand the outlet point, wherein the return pointis blocked.

shows a partial side view of the pot-like housing partof the plate-like housing part. The view plane ofis parallel to the flat contact surface.

The three receiving bores;andare arranged side-by-side in a direction parallel to the control axis (no.in). A straight second boreleads from the contact surfaceto the input pointof the receiving boreof the third control assembly. The opening of the second bore at the contact surfaceforms the transfer point. There, the pressurized fluid flowing in from the auxiliary pump is transferred from the plate-like housing partto the pot-like housing part.

The straight first boreis drilled infrom the left, running parallel to the control axis. The insertion opening for the drills is closed with a separate locking screw. The first boreintersects all three receiving bores;;, with reference being made to the statements offor further details.

A straight fourth boreleads from the third measuring connectionto the first bore. The fourth boreis arranged inclined such that the corresponding drill is can be inserted from the third measuring connection, wherein the circle cylinder defined by the drill does not intersect the third measuring connection. Similarly, a straight third boreleads from the first or second measuring connections;to the receiving boreand.

shows a partial sectional view of the pot-like housing partin the area of the receiving boreof the third control assembly. The sectional plane is aligned perpendicular to the control axis (no.in) containing the central axisof the receiving bore. The receiving boreof the third control assembly is formed as a stepped bore, each step forming a different connection point;;. The receiving borepenetrates the wall of the pot-like housing part, so that it directly opens into the interiorof the housing.

The step with the largest diameter, which is arranged on the outside of the pot-like housing part, forms the inlet pointof the third control assembly. There, the second boreopens.

The step with the smallest diameter, which is arranged inside the pot-like housing part, forms the return pointof the third control assembly, which is permanently connected to the interiorof the housing.

The step arranged between them in the direction of the central axis, which has an average diameter, forms the outlet pointof the third control assembly. There, the first boreintersects the receiving bore, being arranged approximately tangential to the cylindrical wall surface of the outlet pointof the third control assembly.

shows a partial sectional view of the pot-like housing partin the area of the receiving boreof the first control assembly. The sectional plane is aligned perpendicular to the control axiscontaining the central axis of the third bore. As the third boreopens slightly off-center into the receiving boreof the first control assembly, the said receiving boredoes not appear with its full diameter in.

First, it can be seen inthat the first measuring connectionis drilled such that it directly intersects the first control chamber. However, it is also contemplated that the corresponding permanent connection will be made via a further bore. The third boreextends from the first measuring connectionin a straight line to the output pointof the first control assembly.

The receiving boreis configured in the form of a stepped bore. The respective steps of different diameters form the connection point;;. The inlet pointof the first control assembly is formed by the outermost and therefore largest diameter step in relation to the central axis. There, the first boreopens, preferably substantially centrally. The furthest inside and thus smallest diameter step forms the return pointof the first control assembly. This is connected to the interiorof the housingvia a channel, which runs parallel to the control axis (no.in).

The output pointof the first control assembly is arranged in the direction of the central axisbetween the inlet pointand the return point. Accordingly, this has an average diameter. There, the third boreopens, preferably slightly off-center.